Hello and welcome to Petco Pet Education Center, formerly Petcoach. The lump there could be from many different causes: 1. infected ball of pus under the skin from a previous wound. 2. A foreign object stuck under the skin from the wound 3. A lump there unrelated to the wound (lipoma, tumor, etc.) 4. Scar tissue and non-infected inflammation secondary to the wound. 5. Other causes.
From the image the little red bit is suggestive that there might be a component of infection/inflammation ongoing, but overall it doesn't appear very angry or inflamed.
Ideally I would recommend having it seen, and your vet will likely put a needle into it to see if it is a ball of infection or something else.
Otherwise, if it isn't bothering Chase you can monitor it for now, and if it is getting smaller/going away don't worry, but if it is growing or hasn't started to shrink in 5-7 days I would get it checked.